Control system for an N-methyl-2-pyrrolidone refining unit receiving heavy sweet charge oil

ABSTRACT

A refining unit treats heavy sweet charge oil with a methyl-2-pyrrolidone solvent, hereafter referred to as MP, in a refining tower to yield raffinate and extract mix. The MP is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a refractometer, a sulfur analyzer and viscosity analyzers; all sampling the heavy sweet charge oil and providing corresponding signals. Sensors sense the flow rates of the charge oil and the MP flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the heavy sweet charge oil and the MP flow rates is controlled in accordance with the signals from all the analyzers, the refractometer and all the sensors, while the other flow rate of the heavy sweet charge oil and the MP flow rates is constant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to control systems and methods in generaland, more particularly, to control systems and methods for oil refiningunits.

SUMMARY OF THE INVENTION

A refining unit treats heavy sweet charge oil withN-methyl-2-pyrrolidone solvent, hereafter referred to as MP, in anextractor to yield raffinate and extract mix. The MP is recovered fromthe raffinate and from the extract mix and returned to the extractor. Asystem controlling the refining unit includes a gravity analyzer, arefractometer, a sulfur analyzer and viscosity analyzers. The analyzersand the refractometer sample the heavy sweet charge oil and providecorresponding signals. Sensors sense the flow rates of the charge oiland the MP flowing into the refining tower and the temperature of theextract mix and provide corresponding signals. The flow rate of theheavy sweet charge oil or the MP is controlled in accordance with thesignals provided by all the sensors and the analyzers while the otherflow rate of the heavy sweet charge oil and the furfural flow rates isconstant.

The objects and advantages of the invention will appear more fullyhereinafter from a consideration of the detailed description whichfollows, taken together with the accompanying drawings wherein oneembodiment of the invention is illustrated by way of example. It is tobe expressly understood, however, that the drawings are for illustrationpurposes only and are not to be construed as defining the limits of theinvention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a refining unit in partial schematic form and a controlsystem, constructed in accordance with the present invention, in simpleblock diagram form.

FIG. 2 is a detailed block diagram of the control means shown in FIG. 1.

FIGS. 3 through 13 are detailed block diagrams of the H computer, the Ksignal means, the H signal means, the KV computer, the VI signal means,the SUS computer, the SUS₂₁₀ computer, the VI_(DWC).sbsb.O computer, theVI_(DWC).sbsb.P computer, the ΔRI computer and the J computer,respectively, shown in FIG. 2.

DESCRIPTION OF THE INVENTION

An extractor 1 in a refining unit is receiving heavy sweet charge oil byway of a line 4 and N-methyl-2-pyrrolidone solvent, hereafter referredto as MP, by way of a line 7 and providing raffinate to recovery by wayof a line 10, and an extract mix to recovery by way of a line 14.

Heavy sweet charge oil is a charge oil having a sulfur content less thana predetermined sulfur content and having a kinematic viscosity,corrected to a predetermined temperature, greater than a predeterminedkinematic viscosity. Preferably, the predetermined sulfur content is1.0%, the predetermined temperature is 210° F., and the predeterminedkinematic viscosity is 15.0, respectively. The temperature is extractor1 is controlled by cooling water passing through a line 16. A gravityanalyzer 20, a refractometer 22, viscosity analyzers 23 and 24, and asulfur analyzer 28 sample the charge oil in line 4 and provide signalsAPI, RI, KV₂₁₀, KV₁₅₀ and S, respectively, corresponding to the APIgravity, the refractive index, the kinematic viscosity at 210° F. and150° F., and the sulfur content, respectively, of the heavy sweet chargeoil.

A flow transmitter 30 in line 4 provides a signal CHG corresponding tothe flow rate of the charge oil in line 4. Another flow transmitter 33in line 7 provides a signal SOLV corresponding to the MP flow rate. Atemperature sensor 38, sensing the temperature of the extract mixleaving extractor 1, provides a signal T corresponding to the sensedtemperature. All signals hereinbefore mentioned are provided to controlmeans 40.

Control means 40 provides signal C to a flow recorder controller 43.Recorder controller 43 receives signals CHG and C and provides a signalto a valve 48 to control the flow rate of the charge oil in line 4 inaccordance with signals CHG and C so that the charge oil assumes adesired flow rate. Signal T is also provided to temperature controller50. Temperature controller 50 provides a signal to a valve 51 to controlthe amount of cooling water entering extractor 1 and hence thetemperature of the extract-mix in accordance with its set point positionand signal T.

The following equations are used in practicing the present invention forheavy sweet charge oil:

    H.sub.210 =1n1n(KV.sub.210 +C.sub.1)                       (1)

where H₂₁₀ is a viscosity H value for 210° F., KV₂₁₀ is the kinematicviscosity of the charge oil at 210° F. and C₁ is a constant having apreferred value of 0.6.

    H.sub.150 =1n1n(KV.sub.150 +C.sub.1)                       (2)

where H₁₅₀ is a viscosity H value for 150° F., and KV₁₅₀ is thekinematic viscosity of the charge oil at 150° F.

    K.sub.150 =[C.sub.2 -1n(T.sub.150 +C.sub.3 ]/C.sub.4       (3)

where K₁₅₀ is a constant needed for estimation of the kinematicviscosity at 100° F., T₁₅₀ is 150, and C₂ through C₄ are constantshaving preferred values of 6.5073, 460 and 0.17937, respectively.

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150     (4)

where H₁₀₀ is a viscosity H value for 100° F.

    KV.sub.100 =exp[exp(H.sub.100)]-C.sub.1,                   (5)

where KV₁₀₀ is the kinematic viscosity of the charge oil at 100° F.

    SUS=C.sub.5 (KV.sub.210)+[C.sub.6 +C.sub.7 (KV.sub.210)]/[C.sub.8 +C.sub.9 (KV.sub.210)+C.sub.10 (KV.sub.210).sup.2 +C.sub.11 (KV.sub.210).sup.3 ](C.sub.12),                                              (6)

where SUS is the viscosity in Saybolt Universal Seconds and C₅ throughC₁₂ are constants having preferred values of 4.6324, 1.0, 0.03264,3930.2, 262.7, 23.97, 1.646 and 10⁻⁵, respectively.

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS,

where SUS₂₁₀ is the viscosity in Saybolt Universal Seconds at 210° F.and C₁₃ through C₁₆ are constants having preferred values of 1.0,0.000061, 210 and 100, respectively.

    VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (RI)+C.sub.19 (API).sup.2 -C.sub.20 (RI)(S)+C.sub.21 (KV.sub.210)(VI)+C.sub.22 (KV.sub.210)(S), (8)

where VI_(DWC).sbsb.O is the viscosity index of dewaxed charge oil at 0°F. and C₁₇ through C₂₂ are constants having preferred values of 600.63,434.96, 0.14988, 6.9334, 0.01532 and 0.79708, respectively.

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +[Pour][C.sub.23 -C.sub.24 1nSUS.sub.210 +C.sub.25 (1nSUS.sub.210).sup.2 ],          (9)

where VI_(DWC).sbsb.P and Pour are the viscosity index of the dewaxedheavy sweet charge oil at a predetermined temperature and the Pour Pointof the dewaxed product, respectively, and C₂₃ through C₂₅ are constantshaving preferred values of 2.856, 1.18 and 0.126, respectively.

    ΔVI=VI.sub.RO -VI.sub.DWC.sbsb.O =VI.sub.RP -VI.sub.DWC.sbsb.P, (10)

where VI_(RO) and VI_(RP) are the VI of the refined oil at 0° F., andthe predetermined temperature, respectively.

    ΔRI=[-C.sub.26 +C.sub.27 (API).sup.2 -C.sub.28 (S).sup.2 +C.sub.29 (ΔVI)(KV.sub.210)+C.sub.30 (ΔVI)(S)+C.sub.31 (KV.sub.210)(S)]C.sub.32,                                 (11)

where ΔRI is the change in the refractive index between the heavy sweetcharge oil and the raffinate and C₂₆ through C₃₂ are constants havingpreferred values of 436.46, 0.89521, 11.537, 0.26756, 0.96234, 3.007 and10⁻⁴, respectively.

    J=-C.sub.33 +C.sub.34 (ΔVI)+C.sub.35 (T).sup.2 -C.sub.36 (S)+C.sub.37 (ΔRI)(ΔVI)+C.sub.38 (ΔVI)(T),           (12)

where J is the methyl-2-pyrrolidone dosage and C₃₃ through C₃₈ areconstants having preferred values of 363.41, 37.702, 0.020911, 492.43,543.2 and 0.27069, respectively.

    C=(SOLV)(100)/J                                            (13)

where C is the new charge oil flow rate.

Referring now to FIG. 2, signal KV₂₁₀ is provided to an H computer 50 incontrol means 40, while signal KV₁₅₀ is applied to an H computer 50A. Itshould be noted that elements having a number and a letter suffix aresimilar in construction and operation as to those elements having thesame numeric designation without a suffix. All elements in FIG. 2,except elements whose operation is obvious, will be disclosed in detailhereinafter. Computers 50 and 50A provide signals E₁ and E₂corresponding to H₂₁₀ and H₁₅₀, respectively, in equations 1 and 2,respectively, to H signal means 53. K signal means 55 provides a signalE₃ corresponding to the term K₁₅₀ in equation 3 to H signal means 53. Hsignal means 53 provides a signal E₄ corresponding to the term H₁₀₀ inequation 4 to a KV computer 60 which provides a signal E₅ correspondingto the term KV₁₀₀ in accordance with signal E₄ and equation 5 ashereinafter explained.

Signals E₅ and KV₂₁₀ are applied to VI signal means 63 which provides asignal E₆ corresponding to the viscosity index.

An SUS computer 65 receives signal KV₂₁₀ and provides a signal E₇corresponding to the term SUS in accordance with the received signalsand equation 6 as hereinafter explained.

An SUS 210 computer 68 receives signal E₇ and applies signal E₈corresponding to the term SUS₂₁₀ in accordance with the received signaland equation 7 as hereinafter explained.

A VI_(DWC).sbsb.O computer 70 receives signal RI, S, API, KV₂₁₀ and E₆and provides a signal E₁₀ corresponding to the term VI_(DWC).sbsb.O inaccordance with the received signals and equation 8 as hereinafterexplained.

A VI_(DWC).sbsb.P computer 72 receives signal E₈ and E₁₀ and provides asignal E₁₁ corresponding to the term VI_(DWC).sbsb.P in accordance withthe received signals and equation 9. Subtracting means 76 performs thefunction of equation 10 by subtracting signal E₁₁ from a direct currentvoltage V₉, corresponding to the term VI_(RP), to provide a signal E₁₂corresponding to the term ΔVI in equation 10.

A ΔRI computer 79 receives signals KV₂₁₀, API, S and ΔVI and provides asignal ΔRI corresponding to the term ΔRI in equation 11, in accordancewith the received signals and equation 11 as hereinafter explained.

A J computer 80 receives signals T, ΔRI, S and E₁₂ and provide a signalE₁₃ corresponding to the term J in accordance with the received signalsand equation 12 as hereinafter explained to a divider 83.

Signal SOLV is provided to a multiplier 82 where it is multiplied by adirect current voltage V₂ corresponding to a value of 100 to provide asignal corresponding to the term (SOLV)(100) in equation 13. The productsignal is applied to divider 83 where it is divided by signal E₁₃ toprovide signal C corresponding to the desired new charge oil flow rate.

It would be obvious to one skilled in the art that if the charge oilflow rate was maintained constant and the methyl-2-pyrrolidone flow ratevaried, equation 13 would be rewritten as

    SO=(J)(CHG)/100                                            (14)

where SO is the new methyl-2-pyrrolidone flow rate. Control means 40would be modified accordingly.

Referring now to FIG. 3, H computer 50 includes summing means 112receiving signal KV₂₁₀ and summing it with a direct current voltage C₁to provide a signal corresponding to the term [KV₂₁₀ +C₁ ] shown inequation 1. The signal from summing means 112 is applied to a naturallogarithm function generator 113 which provides a signal correspondingto the natural log of the sum signal which is then applied to anothernatural log function generator 113A which in turn provides signal E₁.

Referring now to FIG. 4, K signal means 55 includes summing means 114summing direct current voltages T₁₅₀ and C₃ to provide a signalcorresponding to the term [T₁₅₀ +C₃ ] which is provided to a natural logfunction generator 113B which in turn provides a signal corresponding tothe natural log of the sum signal from summing means 114. Subtractingmeans 115 subtracts the signal provided by function generator 113B froma direct current voltage C₂ to provide a signal corresponding to thenumerator of equation 3. A divider 116 divides the signal fromsubtracting means 115 with a direct current voltage C₄ to provide signalE₃.

Referring now to FIG. 5, H signal means 53 includes subtracting means117 which subtracts signal E₁ from signal E₂ to provide a signalcorresponding to the term H₁₅₀ -H₂₁₀, in equation 4, to a divider 118.Divider 118 divides the signal from subtracting means 117 by signal E₃.Divider 114 provides a signal which is summed with signal E₁ by summingmeans 119 to provide signal E₄ corresponding to H₁₀₀.

Referrning now to FIG. 6, a direct current voltage V₃ is applied to alogarithmic amplifier 120 in KV computer 60. Direct current voltage V₃corresponds to the mathematical constant e. The output from amplifier120 is applied to a multiplier 122 where it is multiplied with signalE₄. The product signal from multiplier 122 is applied to an antilogcircuit 125 which provides a signal corresponding to the term exp (H₁₀₀)in equation 5. The signal from circuit 125 is multiplied with the outputfrom logarithmic amplifier 120 by a multiplier 127 which provides asignal to antilog circuit 125A. Circuit 125A is provided to subtractingmeans 128 which subtracts a direct current voltage C₁ from the signalfrom circuit 125A to provide signal E₅.

Referring now to FIG. 7, VI signal means 63 is essentially memory meanswhich is addressed by signals E₅, corresponding to KV₁₀₀, and signalKV₂₁₀. In this regard, a comparator 130 and comparator 130A represent aplurality of comparators which receive signal E₅ and compare signal E₅to reference voltages, represented by voltages R₁ and R₂, so as todecode signal E₅. Similarly, comparators 130B and 130C represent aplurality of comparators receiving signal KV₂₁₀ which compare signalKV₂₁₀ with reference voltages RA and RB so as to decode signal KV₂₁₀.The outputs from comparators 130 and 130B are applied to an AND gate 133whose output controls a switch 135. Thus, should comparators 130 and130B provide a high output, AND gate 133 is enabled and causes switch135 to be rendered conductive to pass a direct current voltage V_(A)corresponding to a predetermined value, as signal E₆ which correspondsto VI. Similarly, the outputs of comparators 130 and 130C control an ANDgate 133A which in turn controls a switch 135A to pass or to block adirect current voltage V_(B). Similarly, another AND gate 133B iscontrolled by the outputs from comparators 130A and 130B to control aswitch 135B so as to pass or block a direct current voltage V_(C).Again, an AND gate 133C is controlled by the outputs from comparators130A and 130C to control a switch 135C to pass or to block a directcurrent voltage V_(D). The outputs of switches 135 through 135C are tiedtogether so as to provide a common output.

Referring now to FIG. 8, the SUS computer 65 includes multipliers 136,137 and 138 multiplying signal KV₂₁₀ with direct current voltages C₉, C₇and C₅, respectively, to provide signals corresponding to the terms C₉(KV₂₁₀), C₇ (KV₂₁₀) and C₅ (KV₂₁₀), respectively in equation 6. Amultiplier 139 effectively squares signal KV₂₁₀ to provide a signal tomultipliers 140, 141. Multiplier 140 multiplies the signal frommultiplier 139 with a direct current voltage C₁₀ to provide a signalcorresponding to the term C₁₀ (KV₂₁₀)² in equation 6. Multiplier 141multiplies the signal from multiplier 139 with signal KV₂₁₀ to provide asignal corresponding to (KV₂₁₀)³. A multiplier 142 multiplies the signalfrom multiplier 141 with a direct current voltage C₁₁ to provide asignal corresponding to the term C₁₁ (KV₂₁₀)³ in equation 6. Summingmeans 143 sums the signals from multipliers 136, 140 and 142 with adirect current voltage C₈ to provide a signal to a multiplier 144 whereit is multiplied with a direct current voltage C₁₂. The signal frommultiplier 137 is summed with a direct current voltage C₆ by summingmeans 145 to provide a signal corresponding to the term [C₆ +C₇ (KV₂₁₀]. A divider 146 divide the signal provided by summing means 145 withthe signal provided by multiplier 144 to provide a signal which issummed with the signal from multiplier 138 by summing means 147 toprovide signal E₇.

Referring now to FIG. 9, SUS₂₁₀ computer 68 includes subtracting means148 which subtracts a direct current voltage C₁₆ from another directcurrent voltage C₁₆ from another direct current voltage C₁₅ to provide asignal corresponding to the term (C₁₅ -C₁₆) in equation 7. The signalfrom subtracting means 148 is multiplied with a direct current voltageC₁₄ by a multiplier 149 to provide a product signal which is summed withanother direct current voltage C₁₃ by summing means 150. Summing means150 provides a signal corresponding to the term [C₁₃ +C₁₄ (C₁₅ -C₁₆ ] inequation 7. The signal from summing means 150 is multiplied with signalE₇ by a multiplier 152 to provide signal E₈.

Referring now to FIG. 10, multipliers 155, 156 multiply signal RI with adirect current voltage C₁₈ and signal S, respectively, to provideproduct signals. Multipliers 159, 160 multiply signal KV₂₁₀ with signalsS and E₆, respectively, to provide product signals. Multiplier 163effectively squares signal API. Multipliers 166, 167, 168 and 169multiply signals from multipliers 156, 159, 160 and 163, respectively,with direct current voltages C₂₀, C₂₂, C₂₁ and C₁₉, respectively, toprovide signals corresponding to the term C₂₀ (RI)(S), C₂₂ (KV₂₁₀)(S),C₂₁ (KV₂₁₀)(VI) and C₁₉ (API)², respectively, in equation 8. Summingmeans 173 effectively sums the positive terms of equation 8 when it sumsa direct current voltage C₁₇ with signals from multipliers 167, 168 and169 to provide a sum signal to subtracting means 175. Summing means 177effectively sums the negative terms in equation 8 when it sums thesignals from multipliers 165, 166 to provide a signal to subtractingmeans 175 where it is subtracted from the signal from summing means 173.Subtracting means 175 provides signal E₁₀.

VI_(DWC).sbsb.P computer 72 shown in FIG. 11, includes a naturallogarithm function generator 200 receiving signal E₈ and providing asignal corresponding to the term 1nSUS₂₁₀ to multipliers 201 and 202.Multiplier 201 multiplies the signal from function generator 200 with adirect current voltage C₂₄ to provide a signal corresponding to the termC₂₄ 1nSUS₂₁₀ in equation 9. Multiplier 202 effectively squares thesignal from function generator 200 to provide a signal that ismultiplied with the direct current voltage C₂₅ by a multiplier 205.Multiplier 205 provides a signal corresponding to the term C₂₅(1nSUS₂₁₀)² in equation 9. Subtracting means 206 subtracts the signalsprovided by multiplier 201 from the signal provided by multiplier 205.Summing means 207 sums the signal from subtracting means 206 with adirect current voltage C₂₃. A multiplier 208 multiplies the sum signalfrom summing means 207 with a direct current voltage POUR to provide asignal which is summed with signal E₁₀ by summing means 210 whichprovides signal E₁₁.

Referring now to FIG. 12, ΔRI computer 78 includes multipliers 180, 181which effectively squares signals S, API to provide product signals tomultipliers 183 and 184, respectively, where they are multiplied withdirect current voltages C₂₈ and C₂₇, respectively. Multipliers 183 and184 provide signals corresponding to the terms C₂₈ (S)² and C₂₇ (API)²,respectively, in equation 11. Multipliers 186, 187 multiply signal Swith signals KV₂₁₀ and E₁₂ to provide signals to multipliers 190 and191, respectively, where they are multiplied with direct current voltageC₃₁ and C₃₀, respectively. Multipliers 190, 191 provide signalscorresponding to the terms C₃₁ (KV₂₁₀)(S) and C₃₀ (ΔVI)(S),respectively. A multiplier 194 multiplies signals KV₂₁₀, E₁₂ to providea signal to another multiplier 196 where it is multiplied with a directcurrent voltage C₂₉ to provide a signal corresponding to the term C₂₉(ΔVI)(KV₂₁₀). Summing means 200 effectively sums the positive term ofequation 11 when it sums signals from multipliers 184, 190, 191 and 196to provide a sum signal to subtracting means 201. Summing means 203effectively sums the negative terms of equation 11 when it sums a directcurrent voltage C₂₆ with the signal from multiplier 183 to provide asignal which is subtracted from the signal provided by summing means 200by subtracting means 201. Subtracting means 201 provides a signal whichis multiplied with a direct current voltage C₃₂ by a multiplier 205 toprovide signal ΔRI.

Referring now to FIG. 13, J computer 80 includes multipliers 210, 211and 212 multiplying signals E₁₂ with signals ΔRI and T and a directcurrent voltage C₃₄, respectively. A multiplier 214 effectively squaressignal T and provides it to another multiplier 215 where it ismultiplied with a direct current voltage C₃₅. Multiplier 215 provides asignal corresponding to the term C₃₅ (T)² in equation 12. A multiplier218 multiplies signal S with a direct current voltage C₃₆ to provide asignal corresponding to the term C₃₆ (S) in equation 12. Multipliers220, 221 multiplies the signals from multipliers 210 and 211,respectively, with direct current voltages C₃₇ and C₃₈, respectively, toprovide signals corresponding to the term C₃₇ (ΔRI)(ΔVI) and C₃₈(ΔVI)(T), respectively, in equation 12. Summing means 225 effectivelysums the positive terms in equation 12 when it sums the signals frommultipliers 212, 215, 220 and 221 to provide a sum signal. Summing means227 effectively sums the negative terms of equation 12 when it sums thesignal from multiplier 218 with a direct current voltage C₃₃.Subtracting means 230 subtracts the signal from summing means 227 fromthe signal provided by summing means 225 to provide signal E₁₃corresponding to the methyl-2-pyrrolidone dosage.

The present invention as hereinbefore described controls an MP refiningunit receiving heavy sweet charge oil to achieve a desired charge oilflow rate for a constant MP flow rate. It is also within the scope ofthe present invention, as hereinbefore described, to control the MP flowrate while the heavy sweet charge oil flow is maintained at a constantrate.

What is claimed is:
 1. A control system for a refining unit receivingheavy sweet charge oil and N-methyl-2-pyrrolidone solvent, one of whichis maintained at a fixed rate while the flow rate of the other iscontrolled by the control system, wherein said refining unit treats thereceived heavy sweet charge oil with the received N-methyl-2-pyrrolidoneto yield extract mix and raffinate which is subsequently processed toyield refined oil, comprising gravity analyzer means for sampling theheavy sweet charge oil and providing a signal API corresponding to theAPI gravity of the heavy sweet charge oil; refractometer means forsampling the heavy sweet charge oil and providing a signal RIcorresponding to the refractive index of the heavy sweet charge oil;viscosity analyzer means for sampling the heavy sweet charge oil andproviding signals KV₁₅₀ and KV₂₁₀ corresponding to the kinematicviscosities, corrected to 150° F. and 210° F., respectively; sulfuranalyzer means for sampling the heavy sweet charge oil and providing asignal S corresponding to the sulfur content of the heavy sweet chargeoil; flow rate sensing means for sensing the flow rates of the heavysweet charge oil and of the N-methyl-2-pyrrolidone and providing signalsCHG and SOLV, corresponding to the charge oil flow rate and theN-methyl-2-pyrrolidone flow rate respectively; temperature sensing meanssensing the temperature of the extract mix and providing a correspondingsignal T; and control means connected to all of the analyzer means, tothe refractometer means and to all the sensing means for controlling theother flow rate of the heavy sweet charge oil and theN-methyl-2-pyrrolidone flow rate in accordance with signals API, RI,KV₁₅₀, KV₂₁₀, S, T, CHG and SOLV, wherein said control means includes VIsignal means connected to the viscosity analyzer means for providing asignal VI corresponding to the viscosity index of the heavy sweet chargeoil in accordance with kinematic viscosity signals KV₁₅₀ and KV₂₁₀,SUS₂₁₀ signal means connected to the viscosity analyzer means forproviding a signal SUS₂₁₀ corresponding to the heavy sweet charge oilviscosity in Saybolt Universal Seconds corrected to 210° F., ΔVI signalmeans connected to the viscosity analyzer means, to the gravity analyzermeans, to the refractometer means, to the VI signal means, to the sulfuranalyzer means and the SUS₂₁₀ signal means and receiving a DC voltageVI_(RP) for providing a signal ΔVI corresponding to the change inviscosity index in accordance with signals KV₂₁₀, API, VI, RI, S andSUS₂₁₀ and voltage VI_(RP), ΔRI signal means connected to the gravityanalyzer means, to the viscosity analyzer means, to the sulfur analyzermeans, and to the ΔVI signal means for providing a signal ΔRIcorresponding to a change in refractive index between the heavy sweetcharge oil and the raffinate, J signal means receiving direct currentvoltages corresponding to constants C₃₃ through C₃₈ and being connectedto the VI signal means, to the ΔRI signal means, to the temperaturesensing means and to the sulfur analyzer means for providing a J signalcorresponding to an N-methyl-2-pyrrolidone dosage J for heavy sweetcharge oil in accordance with the signals ΔVI, ΔRI, S and T, thereceived voltages and the following equation:

    J=-C.sub.33 +C.sub.34 (ΔVI)+C.sub.35 (T).sup.2 -C.sub.36 (S)+C.sub.37 (ΔRI)(ΔVI)+C.sub.38 (ΔVI)(T),

control signal means connected to the J signal means and to the flowrate sensing means for providing a control signal in accordance with theJ signal and one of the sensed flow rate signals, and apparatus meansconnected to the control signal means for controlling the one flow rateof the heavy sweet charge oil and N-methyl-2-pyrrolidone flow rates inaccordance with the control signal.
 2. A system as described in claim 1in which the SUS₂₁₀ signal means includes SUS signal means connected tothe viscosity analyzer means, and receiving direct current voltagescorresponding to constants C₅ through C₁₂ for providing a signal SUScorresponding to an interim factor SUS in accordance with signal KV₂₁₀,the received voltages and the following equation:

    SUS=C.sub.5 (KV.sub.210)+[C.sub.6 +C.sub.7 (KV.sub.210)]/[C.sub.8 +C.sub.9 (KV.sub.210)+C.sub.10 (KV.sub.210).sup.2 +C.sub.11 (KV.sub.210).sup.3 ](C.sub.12),

and SUS₂₁₀ network means connected to the SUS signal means and to theΔVI signal means and receiving direct current voltages corresponding toconstants C₁₃ through C₁₆ for providing signal SUS₂₁₀ to the ΔVI signalmeans in accordance with signal SUS, the receiving voltages and thefollowing equation:

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS.


3. A system as described in claim 2 in which the VI signal meansincludes K signal means receiving direct current voltages correspondingto constants C₂, C₃, C₄ and to a temperature T₁₅₀ of 150° F. forproviding a signal K₁₅₀ corresponding to the kinematic viscosity of thecharge oil corrected to 150° F. in accordance with the received voltagesand the following equation:

    K.sub.150 =[C.sub.2 -1n(T.sub.150 +C.sub.3)]/C.sub.4 ;

H₁₅₀ signal means connected to the viscosity analyzer means andreceiving a direct current voltage corresponding to a constant C₁ forproviding a signal H₁₅₀ corresponding to a viscosity H value for 150° F.in accordance with signal KV₁₅₀, the received voltage C₁ and thefollowing equation:

    H.sub.150 =1n1n(KV.sub.150 +C.sub.1);

H₂₁₀ signal means connected to the viscosity analyzer means andreceiving the voltage corresponding to the constant C₁ for providingsignal H₂₁₀ corresponding to a viscosity H value for 210° F. inaccordance with signal KV₂₁₀, the received voltage and the followingequation:

    H.sub.210 =1n1n(KV.sub.210 +C.sub.1);

H₁₀₀ signal means connected to the K signal means, to the H₁₅₀ signalmeans and the H₂₁₀ signal means for providing a signal H₁₀₀corresponding to a viscosity H value for 100° F., in accordance withsignals H₁₅₀, H₂₁₀ and K₁₅₀ and the following equation:

    H.sub.100 =H.sub.200 +(H.sub.150 -H.sub.210)/K.sub.150 ;

KV₁₀₀ signal means connected to the H₁₀₀ signal means and receiving thevoltage corresponding to the constant C₁ for providing a signal KV₁₀₀corresponding to a kinetic viscosity for the charge oil corrected to100° F. in accordance with signal H₁₀₀, the received voltage, and thefollowing equation:

    KV.sub.100 =exp[exp(H100)]-C.sub.1 ;

and VI memory means connected to the KV₁₀₀ signal means and to theviscosity analyzer means having a plurality of signals stored therein,corresponding to different viscosity indexes and controlled by signalsKV₁₀₀ and KV₂₁₀ to select a stored signal and providing the selectedstored signal as signal VI.
 4. A system as described in claim 3 in whichthe ΔVI signal means includes VI_(DWC).sbsb.O signal means connected tothe viscosity analyzer means, to the gravity analyzer means, to thesulfur analyzer means, to the VI signal means, to the refractometermeans and receiving direct current voltages corresponding to constantsC₁₇ through C₂₂ for providing a signal VI_(DWC).sbsb.O in accordancewith signals KV₂₁₀, VI, API, RI and S, the received voltages and thefollowing equation:

    VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (RI)+C.sub.19 (API).sup.2 -C.sub.20 (RI)(S)+C.sub.21 (KV.sub.210)(VI)+C.sub.22 (KV.sub.210)(S),

a VI_(DWC).sbsb.P signal means connected to the VI_(DWC).sbsb.O signalmeans connected to the VI_(DWC).sbsb.O signal means and to the SUS₂₁₀signal means, and receiving direct current voltages corresponding toconstants C₂₃ through C₂₅ and to the pour point of the refined oil forproviding a signal VI_(DWC).sbsb.P in accordance with signalsVI_(DWC).sbsb.O and SUS₂₁₀, the received voltages, and the followingequation:

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(POUR)[C.sub.23 -C.sub.24 1nSUS.sub.210 +C.sub.25 (1nSUS.sub.210).sup.2 ],

and subtracting means connected to the VI_(DWC).sbsb.P signal means andto the J signal means and receiving direct voltage VI_(RP) forsubtracting signal VI_(DWC).sbsb.P from voltage VI_(RP) to provide theΔVI signal to the J signal means.
 5. A system as described in claim 4 inwhich the ΔRI signal means also receives direct current voltagescorresponding to the constants C₂₆ through C₃₂ and provides signal ΔRIin accordance with the received voltages, signals API, S, ΔVI and KV₂₁₀and the following equation:

    ΔRI=[-C.sub.26 +C.sub.27 (API).sup.2 -C.sub.28 (S)+C.sub.29 (ΔVI)(KV.sub.210)+C.sub.30 (ΔVI)(S)+C.sub.31 (KV.sub.210)(S)]C.sub.32.


6. A system as described in claim 5 in which the flow rate of the heavysweet charge oil is controlled and the flow of theN-methyl-2-pyrrolidone is maintained at a constant rate and the controlsignal means receives signal SOLV from the flow rate sensing means, theJ signal from the J signal means and a direct current voltagecorresponding to a value of 100 and provides a signal C to the apparatusmeans corresponding to a new heavy sweet charge oil flow rate inaccordance with the J signal, signal SOLV and the received voltage andthe following equation:

    C=(SOLV)(100)/J,

so as to cause the apparatus means to change the heavy sweet charge oilflow to the new flow rate.
 7. A system as described in claim 5 in whichthe controlled flow rate is the N-methyl-2-pyrrolidone flow rate and theflow of the heavy sweet charge oil is maintained constant, and thecontrol signal means is connected to the sensing means, to the J signalmeans and receives a direct current voltage corresponding to the valueof 100 for providing a signal SO corresponding to a newN-methyl-2-pyrrolidone flow rate in accordance with signals CHG and Jand received voltage, and the following equation:

    SO=(CHG)(J)/100,

so as to cause the N-methyl-2-pyrrolidone flow to change to the new flowrate.